1. Field of the Invention
The present invention relates to a sheet transport apparatus, an image forming apparatus, and an image reading apparatus, and in particular, to a configuration of a skew feed correcting portion for correcting the skew feed of a sheet.
2. Related Background Art
Conventionally, an image forming apparatus and an image reading apparatus in a printer, a copier, and the like has a sheet transport apparatus for transporting a sheet to an image forming portion or an image reading portion. When a sheet is to be transported in such a sheet transport apparatus, skew may occur in a sheet due to the misalignment of a transport roller, the distortion of a sheet guide, and the like depending on the assembly precision of components.
When an image is formed or an image is read with respect to a sheet transported under the condition of skew feed, a distorted image is formed or read with respect to the sheet. Particularly, in an image forming apparatus having a two-side printing function, an image formed on one surface may be remarkably shifted from an image formed on the other surface.
Therefore, in a conventional sheet transport apparatus, a skew feed correcting portion for correcting the skew feed of a sheet is provided in a sheet transport path. Regarding such a skew feed correcting portion, there are a system using a registration roller, a system of correcting the skew feed of a sheet by pressing a side edge of a sheet into contact with a reference wall provided in parallel to a sheet transport direction at one end of a sheet transport path in a width direction orthogonal to the sheet transport direction as described in Japanese Patent Application Laid-Open No. H09-12182, and the like.
In the case where a sheet jam occurs in the skew feed correcting portion in the sheet transport apparatus, as described in U.S. Pat. No. 6,145,828, the skew feed correcting portion is pulled out, and then, a guide member constituting the upper surface of the sheet transport path is opened, whereby the jammed sheet is removed.
However, in such conventional sheet transport apparatus, image forming apparatus, and image reading apparatus, the lateral length of the guide member constituting the upper surface of the sheet transport path is at least larger than the lateral length of a sheet with a maximum size to be transported. Therefore, the force required for opening the guide member becomes large, degrading operability. In particular, this problem is conspicuous in a sheet transport apparatus with a large size.
Furthermore, even in the case where a jammed sheet is on the front side in a pulling direction of the skew feed correcting portion, in order to open the guide member, the entire skew feed correcting portion needs to be pulled out, which prolongs a time required for jammed sheet processing.